Method of mounting a heater in a tubular cathode

ABSTRACT

METHOD OF MOUNTING A HEATER IN A TUBULAR CATHODE HAVING A CLOSED END IN SUCH A WAY AS TO ASSURE A UNIFORMITY IN THE POSITIONS OF THE HEATERS IN SEVERAL CATHODES AND TO PREVENT CHIPPING AND LOSS OF THE INSULATING COATING ON THE HEATER DURING THE MOUNTING OPERATION. THE METHOD INVOLVES ATTACHING THE ARMS OF A U-SHAPED TAB MEMBER UNIFORMLY TO UNCOATED POTIONS OF THE HEATER LEGS TO PROVIDE A CONVENIENT MANUAL ENGAGEMENT MEANS AND TO RESTRAIN THE LEGS FROM FLARING OUTWARDLY INTO ENGAGEMENT WITH A SHARP EDGE OF THE OPEN END OF THE SLEEVE THROUGH WHICH THE LEGS ARE EXTENDED IN FORMING A HEATER-CATHODE ASSEMBLY. AFTER THE HEATER AND A PORTION OF THE LEGS THEREOF OF THE HEATER-TAB ASSEMBLY HAVE BEEN INSERTED IN THE CATHODE, THE ARMS OF THE U-SHAPED TAB MEMBER ARE WELDED TO HEATER SUPPORT STRUCTURES MOUNTED ON TWO GLASS RODS, AND THE TRANSVERSE PORTION OF THE TAB MEMBER IS REMOVED.

1971 c. L. LUNDVALL n 3,555,640

METHOD OF MOUNTING A HEATER IN A TUBULAR CATHODE Filed Sept. 24, 1968 INVENTOR CARL L.Luuovnl.1. II 94M WM nited States Patent US. Cl. 2925.16 4 Claims ABSTRACT OF THE DISCLOSURE Method of mounting a heater in a tubular cathode having a closed end in such a way as to assure a uniformity in the positions of the heaters in several cathodes and to prevent chipping and loss of the insulating coating on the heater during the mounting operation. The method involves attaching the arms of a U-shaped tab member uniformly to uncoated portions of the heater legs to provide a convenient manual engagement means and to restrain the legs from flaring outwardly into engagement with a sharp edge of the open end of the sleeve through which the legs are extended in forming a heater-cathode assembly. After the heater and a portion of the legs thereof of the heater-tab assembly have been inserted in the cathode, the arms of the U-shaped tab member are welded to heater support structures mounted on two glass rods, and the transverse portion of the tab member is removed.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention relates to a method of mounting a heater in a tubular cathode and particularly concerns a uniform disposition of heaters in a plurality of tubular cathodes with reduced harm to the heaters.

(2) Description of the prior art Heretofore, heaters having an insulating coating thereon and bare leg portions have been inserted into tubular cathodes through an open end thereof, by manually holding the legs and extending the heater through the open end of the cathode. This procedure has been accompanied by several problems.

One problem concerns the degree of the heater exten sion into the cathode. The relatively fine wire of which cathode heaters are usually made requires a very careful manual control in order to avoid deformation of the heater structure. Such required care imposes a limitation on the accuracy with which the degree of extension of the heater into the cathode is effected. It frequently happens, therefore, that in a plurality of heater-cathode assemblies formed by manually extending the heater into the oathode, the heater is differently extended into the cathode.

Where the effective emitting surface of the cathode sleeve is a closed end opposite to the open end thereof through which the heater is extended, the degree of proximity of the heater to such closed end affects the electron emission therefrom. Variations in spacings between the heater and the closed cathode end resulting from the different degrees of extension of the heater into the sleeve, therefore, cause different electron emissions from several cathode-heater assemblies. This is particularly objectionable when the cathodes are used in a three-electron gun system of a color cathode ray tube.

Another problem growing outof the non-uniformity with which heaters are extended into cathodes manually,

resides in a difference in heat output of the heaters of several cathodes. This difference'in heat output is caused by differences in the lengths of the heater wire. The region where lead-ins engage the heater legs are usually "ice fixed, so that dlferent degrees of extension of the heaters into several cathodes will result in engagement of the heater legs by the lead-ins at different longitudinal regions thereof. While the wire of each of several heaters is of exactly the same length, the fixing of the legs at different longitudinal regions thereof to the lead-ins effectively varies the length of the several heaters. Such variations in length of the heaters result in variations in the electrical resistance thereof and consequently a variation in temperature of the several cathodes with which the heaters are associated. This contributes further to variation in electron emission from several cathodes and is particularly objectionable when the heater-cathode assembly is used in a plural gun assembly of a cathode ray tube, as has been pointed out in the foregoing.

A further problem introduced by a manual mounting of a heater in a tubular cathode involves a loss of electrical insulation by the heater during the mounting operation. The legs of the heater are usually relatively long so as to bridge the distance from the cathode to the region of electrical lead-ins to which they are to be fixed as by welding. The portions of the legs adjacent to the cathode when the heater is mounted in the cathode are covered by electrical insulation to prevent heater-to-cathode shorts. Only a relatively short free end portion of the legs are bare to permit electrical engagement with and fixing to lead-in s. In a manual mounting of a heater in a cathode, it is customary to engage the heater legs manually and in this way to support the heater during a mounting operation. However, due to the very small cross sections of the heater legs, it is diflicult to manually engage and hold the heater legs in any precise orientation. Therefore it frequently happens that during the manual engagement, the heater legs are caused to flare outwardly from each other to a degree greater than the diameter of the cathode into which the heater is to be inserted. The edge defining the open heater-receiving end of the cathode is usually relatively sharp and a heater leg when brought into forced engagement therewith during a manual heater mounting step has its electrically insulating coating chipped ofl'. Such removal of the insulating coating from the heater legs gives rise to short circuits between the heater and the cathode.

SUMMARY OF THE INVENTION An improved method of mounting a heater in a cathode is provided. The first step in the method involves forming a subassembly comprising a heater and a U-shaped tab member. The arms of the tab member are mutually spaced a distance less than the diameter of the cathode. The bare end portions of the heater legs are brought into a predetermined engagement with the tab arms, to assure dimensional uniformity among several heater-tab subassemblies, and are fixed thereto as by welding.

In the subassembly so formed, the tab member thereof provides a convenient and rugged portion for manual engagement, While so engaged, the heater is extended into an open end of the cathode. The tab member restrains an outward flaring of the heater legs so that they enter the open cathode without touching the sharp edges there of.

The extending operation may be supplemented by a calibrated force means, such as a spring, for assuringa uniform disposition of heaters in a plurality of cathodes.

After extension of aheater in a cathode in the manner indicated in the foregoing, the arms of the tab member are located adjacent to heater support structures supported on two glass rods. The arms of the tab member are then manually brought into contact with the heater support structures to which they are fixed as by welding.

A plurality of heater-cathode assemblies so formed are uniform in cathode temperature and free fromheat'er-to- 3 cathode shorts during operation. They are, therefore, particularly suited for use in a three-gun assembly of a color cathode ray tube.

IN THE DRAWING FIG. 1 is an elevational view, partly in section, of a heater-cathode assembly of a three-gun cathode ray tube, made in accordance with the invention;

FIG. 2 is a bottom view of the heater-cathode assembly shown in FIG. 1 and depicts three heater-cathode assembli es in a battery of three electron guns;

FIG. 3 is an elevational view of a heater-tab subassembly used in assembling the heater-cathode structure in accordance with the invention;

FIG. 4 is an exploded view of the parts used in forming a heater-cathode assembly in accordance with the invention;

FIG. 5 depicts the step of uniformly controlling the magnitude of extension of the heater into the cathode; and

FIG. 6 shows the U-shaped tab of the heater-tab assembly with its transverse portion removed for electrically isolating the two arms of the tab member.

DETAILED DESCRIPTION The heater-cathode assembly 10 shown in FIG. 1 comprises a tubular cathode 11 having a lower open end 12 and an upper closed end 1-4. Over the upper closed end 14 is a layer 15 of electron emitting material such as combination of barium, calcium and strontium oxides, known in the art. A tubular support for the cathode 11 includes a portion 16 fixed as by welding to the lower end region of the cathode. The upper portion 18 of the support is spaced from the cathode 11 and includes a radiallyextending flange 19 fixed as by welding to tabs 20- imbedded in insulating side support members 22, 24 which may be made of glass, for example. This manner of support of the cathode 11 reduces heat drain from the electron emitting portion 15.

The heater-cathode assembly also includes a heater 26 which may comprise a coiled wire structure coated with insulating material such as aluminum oxide, having leg portions 28, 30 free from insulation. The bare leg portions 28, 30 are fixed as by welding to two metal arms 32, 33 which in turn are fixed as by welding to metallic heater support structures 34, 36 respectively. The support structures 34, 36 are fixed respectively as by welding to metallic support tabs 38, 40 imbedded in the insulating support members 22, 24. Electrical lead wires 42, 44 connect the heater legs 28, 30 to a source, not shown, of suitable electric current.

InFIG, 2 is shown a battery of three heater-cathode assemblies similar to the heater-cathode assembly of FIG. 1 for use in a three-gun battery of a color cathode ray tube. In this battery a third insulating support rod 46 made of glass, for example, is provided. For connecting in series the heater legs 48, 50 of heater-cathode assembly 52 and heater legs 54, 56 of heater-cathode assembly 58 with the heater legs 28, 30 of assembly 10', electrical connectors 59, 60 and heater support structures 61, 62 and 63, 64 may be used, with the heater support structures 34, 36.

In mounting the heater 26 in the cathode 11 (FIG. 1) a. heater-tab subassembly 66 (FIG. 3) is first formed. The heater 26 is usually precision made so that its length, including the bare legs 28, 30, is substantially uniform from heater-to-heater. A U-shaped tab member 68, the arms 32 and 33 of which constitute the tabs thereof, is made. To preserve a desired uniformity in length of the heater-tab subassembly 66, the heater 26 and the U-shaped tab 68 are placed in a suitable welding fixture or jig, not shown, whereby the overall length of the heater-tab assembly and the spacing between the heater legs are accurately determined. With the overall length of the assembly and the leg spacing thus controlled by the Welding fixture, the bare end portions 28, 30 of the heater are fixed as by 4 welding to the arms 32, 33 of the tab member 68. This assures that a plurality of heater-tab assemblies so made will have similar longitudinal dimensions.

After the cathode 11 and the heater supports 34, 36 have been mounted on the tabs 20, 38 and 40, the heatertab assembly 66 is manually engaged by gripping the tab member 68 and advancing the assembly past the heater support structures 34, 36 and into the open end of the cathode 11 (FIG. 4). The advance is continued until opposition to further advance is encountered. While such opposition would appear to indicate that the heater 26 is fully seated in the cathode 11, this may not always be the case, particularly, since it is nearly impossible to use exactly the same force manually in a plurality of heater advance operations.

To assure that the force used in advancing the heater into a cathode is exactly the same in a plurality of heater mounting operations, use may be made of a calibrated spring device 70 shown in FIG. 5. This device may rest on a table 72 and the heater-cathode assembly may be lowered to cause the tab member 68 to come into engagement therewith with suffiicient force to cause the device 70 to register a predetermined force indicated by a calibration 74, for example. Since exactly the same force will be applied to each of a pluraliy of heater-cathode assemblies, there is an assurance of uniformity in the position within the cathodes of a plurality of heaters. The exact force required to fully seat the heater 26 in the cathode 11 and to cause the upper end of the heater 26 to engage the inner surface of the closed end 14 of the cathode 11 (FIG. 1) for maximum heat transfer thereto, may be determined empirically in relation to a predetermined calibration, such as calibration 74 of the device 70, so that when the same force is applied in a number of heater mounting steps, it will assure a full seating of the heater 26 in a cathode 11.

With the heater 26 thus fully seated in the cathode 11, the tab arms 32, 33 are fixed as by welding the heater support structures 34, 36, respectively.

After the tab arms have been fixed to the heater support structures 34, 36, as indicated in the foregoing, the U-shaped tab member 68 is severed, for example, as shown in FIG. 6, to separate a transverse portion 76 from the arms 32, 33. This effectively electrically isolates the arms 32, 33 from each other for permitting suitable electrical energization of the heater 26 (FIG. 1).

The way in which the U-shaped tab member 68 is severed is not critical, so long as the severance results in electrical discontinuity between arms 32, 33. For example, the severance may be eifected by removing a region of the transverse portion 76 extending at right angles to the arms 32, 33.

It will be understood that instead of using three separate metallic elements, e.g. 32, 34 and 38, to mount each heater leg (28) on the glass rod (22), only two elements could be used. For example, element 34 could be com bined with the tab arm 32 as a single piece of metal. Alternatively, elements 38 and 34 could be combined as a single piece.

It is apparent from the foregoing that an improved method of mounting a heater in the tubular cathode is provided, for assuring uniformity in performance of a plurality of heater-cathode assemblies. This is of particular advantage in a three-gun system of a color cathode ray tube.

I claim:

1. In the manufacture of an electron gun structure comprising a pair of insulating supports, a hollow cathode mounted on said supports and a heater element disposed within said cathode and supported independently of said cathode, a method of mounting said heater in said gun structure comprising the steps of:

(a) providing a gun structure comprising a pair of insulating supports, a cup-shaped cathode mounted on said insulating supports, and a pair of heater sup-z ports mounted on said insulating supports independently of said cathode, adjacent to and in a plane spaced from the open end of said cathode,

(b) providing a heater element having two spaced parallel legs,

(c) attaching said heater legs to the two arms of a U-shaped tab member,

((1) then positioning said heater element within said cathode with said tab arms adjacent to said heater supports,

(c) then attaching said tab arms to said heater supports, and

(f) removing a portion of said tab member, leaving the arms thereof disconnected from each other.

2. The method of claim 1 wherein said U-shaped tab member and said heater are supported during said attaching step in such a manner as to define a predetermined overall length of said heater-tab subassembly.

3. Method of mounting a heater having two legs in a tubular cathode having an open end and a closed end,

(a) forming the cathode to a predetermined longitudinal and lateral dimensions,

(b) mounting the cathode on two insulating supports with the open end portion of the cathode extending in a predetermined direction,

(c) mounting two heater support structures on said insulating supports independently of said cathode, in regions spaced from said cathode a predetermined distance in said direction,

(d) attaching the arms of a U-shaped tab member to 30 the two legs of the heater to provide an overall length of the resulting heater-tab assembly substantially equal to the sum of the lengths of said cathode and the distance from the open end of the cathode to an overlapping region of said heater support structures, said heater and array of heater legs in said heatertab subassembly having lateral dimensions for entrance into said open end of the cathode,

(e) then manually engaging said U-shaped tab member and inserting said heater and the portion of said legs into said open end of the cathode with a calibrated force until the arms of said tab member are in overlapping relation with respect to said heater support structures,

(-f) then fixing said tab arms to said heater support structures, and

(g) then severing a portion of said tab member for electrically isolating said arms from each other.

4. The method of claim 1, wherein said heater supports and said tab member are metallic, and said tab arms are Welded to said heater legs and said heater supports.

References Cited UNITED STATES PATENTS 2,386,790 10/1945 Gaun et a]. 29-25.15X 2,508,979 5/1950 Van Gessel. 29-25.13 3,387,166 6/1968 Kraner et a1. 29-25.16X 3,396,298 8/1968 Kuryla t 29-25.11

JOHN F. CAMPBELL, Primary Examiner R. B. LAZARUS, Assistant Examiner US. Cl. X.R. 

